To downsize a sanitary washing device and improve its designability, the downsizing of a water storage tank of a hot water storage-type heat exchanger used in the sanitary washing device is being considered. Conventionally, the water storage tank has been manufactured by vibration welding in which an upper enclosure and a lower enclosure are welded by vibrations. In this method, it is necessary to provide a stroke at the bonding part to vibrate and bond the upper enclosure and the lower enclosure; and it is difficult to downsize the water storage tank. Therefore, a manufacturing method that uses die slide injection (DSI) molding may be considered (JP-A 2008-75426 (Kokai)).
In the manufacturing method using DSI molding, the upper enclosure and the lower enclosure are molded (preliminary molding); subsequently, the dies are caused to slide to align the positions of the upper enclosure and the lower enclosure; and the upper enclosure and the lower enclosure are bonded (secondary molding) by injecting a bonding member between the upper enclosure and the lower enclosure. A stroke is unnecessary in the manufacturing method using DSI molding; therefore, it is easier to downsize the water storage tank than by a manufacturing method using vibration welding.